This invention relates to robotic limbs and, in particular, to a structural design which attempts to be optimally light and simple, for a given rigidity. This design allows lengthening and shortening along the length of the robotic limb, bending and twisting of the robotic limb in any hemispheric direction, and cross-sectional expansion and contraction of the robotic limb. It allows relatively simple open-loop control of these motions.
This invention is expected to work well in applications such as space exploration where weight is an over-riding consideration and in applications such as extremely versatile manipulations of robots of the future.
The prior art includes a number of flexible limbs with multi-articulation units. The following examples have multiple hinges turned by tendon-drive systems: Stelle (U.S. Pat. No. 3,266,059), Anderson (3,497,083), and Wada (U.S. Pat. No. 4,685,349). Examples of gear-driven multiple hinges include Wuenscher (U.S. Pat. No. 3,520,496), Miyake (U.S. Pat. No. 4,568,311), Inoue (U.S. Pat. No. 4,607,578), (U.S. Pat. No. 4,621,965), Hiyane (U.S. Pat. No. 4,697,472), Hodge (U.S. Pat. No. 4,766,775), Akeel (U.S. Pat. No. 4,805,477), Kaufmann (U.S. Pat. No. 4,863,206) and Milenkovic (U.S. Pat. No. 4,907,937). Harwood (U.S. Pat. No. 3,712,481) provides for articulation with rotating wedges. Humphrey (U.S. Pat. No. 4,369,814) utilizes hydraulic action about a slidably anchored gimbal, and Mosher (U.S. Pat. No. 3,580,099) uses hydraulic action about hinged joints.
Hollis (U.S. Pat. No. 4,874,998) utilizes magnetically levitated articulation units, and Larson (U.S. Pat. No. 4,494,417) uses actuators to articulate about double-hemispheric segments. Krue (D.E. 3612-961-A) provides for actuation with hinged double-actuators which interconnect plates to allow articulation. The above patents describe inventions with articulation means that are clearly distinct from the present invention.
There are three related patents in the prior art which are similar in principle to each other, namely Lambert (U.S. Pat. No. 4,651,589), Kimura (U.S. Pat. No. 4,712,969) and Ubhayaker (4,848,179). These utilize three actuators positioned between two plates and connected by universal joints to said two plates. In this configuration, additional provision is required to prevent sliding motion between these two plates, to ensure rigidity of the whole arm structure. Kimura accomplishes this provision in two ways. In his first embodiment he uses an actuator consisting of double-link mechanism which is caused to open and close by a component actuator rotatably attached to the midportion of each link. The fact that the link is a hinge, with a single degree of freedom and the fact that there are three such hinges, configured equilaterally, result in the required additional provision to constrain the two plates from sliding with respect to each other. Lambert has a very similar design incorporating three components which combine actuation and a hinged double-link system.
Ubhayaker uses a similar constraint. In addition to his three actuators, he uses three stabilizer bars which are double links connected to each other by a universal joint and to said two plates by hinged joints. Again, it is the combination of the three hinges that constrain said two plates from sliding with respect to each other.
In Kimura's second embodiment the needed constraint is accomplished by fixedly attaching the bottom of each of the three actuators to the bottom of the two plates.
The advantages of these three embodiments of Kimura and Ubhayaker over the present invention is that only three actuators are required per articulation unit (the present invention requires six). The disadvantages include the fact that the joint at the hinge (with respect to its restriction of the second degree of angular motion) or at the fixed attachment of the actuator to the bottom plate is inherently weaker than the triangular structure with three universal joints, intrinsic to the present invention. This advantage leads to an inherently lighter structure for the present invention. This is, in fact, the basis of the geodesic dome. Another disadvantage is that the additional features of twist and "cross-sectional area" change are not allowed. Also, the amount of angular change is significantly less than is the case with the present invention. Finally, even though there are fewer actuators, the structures of Kimura and Ubhayaker are intrinsically more complicated in the sense of requiring more kinds of components.
Merlet ( WO 89/09120) utilizes six lengthwise elements, connecting base and fore plates, for each articulation unit. However, each of his lengthwise elements is necessarily composed of a separate actuator element connected by a universal joint to a link, whereas in the present invention, a single element, rather than what is, in effect, the double link means of Merlet is used for the lengthwise elements. For these reasons, the present invention is simpler in construction and more versatile in terms of motion capability and range of angular motion per unit length of the flexible limb.
A principle object of the present invention is versatility of motions including length change, angular change in any direction, twisting, and cross-sectional area change. A further object is lightness and optimal rigidity. A further object is modular construction both unit by unit and in terms of components within a unit. A further object is the ability to snake around obstructions. A further object is to provide a limb for grippers. A further object is to provide anchoring capability by wrapping, by insertion and expansion, or by engulfing and contraction. A further object is to provide for simple computer control without the risk of breakage of component elements due to structural over-constraint. A further object is to provide an external skeletal prosthetic device. A further object is to provide for a tapering in terms of articulation unit size and strength along a flexible limb. Finally, a further object is to provide a limb with branching capability, in which smaller flexible limbs branch out from trunk limbs.